Effects of Cementation on the Compressibility of Pierre Shale

Natural cementation in cohesive soils can have a significant effect on the apparent maximum past pressure (¯σvm) estimated from one-dimensional consolidation tests. Relatively small amounts of calcium carbonate (CaCO3), above a threshold value of about 2 percent by weight, appear to cement the structure of a Nebraska Pierre shale, causing measured ¯σvm-values several times larger than the maximum past overburden stress inferred from geological history. However, CaCO3 contents in excess of this threshold value (even up to 50 percent or more) produce little further increase in ¯σvm. On the other hand, leaching out relatively small amounts of CaCo3 from a highly calcareous clay shale can increase its compressibility and produce a lower measured apparent maximum past pressure.